The present invention relates to a fabrication method that prevents cross-contamination in a fabrication process of a semiconductor device containing Ge.
In recent years, examination has been actively made for commercialization of semiconductor devices containing Ge, especially, semiconductor devices using mixed crystal semiconductor materials such as SiGe and SiGeC. In particular, a SiGe mixed crystal semiconductor has a feature of having a band gap narrower than Si and a high hole mobility. By utilizing this feature, for example, by using SiGe mixed crystal as the base layer of a Si bipolar transistor, the high frequency characteristic of the bipolar transistor can be improved. Such a semiconductor device using SiGe has advantages of being inexpensive and easy in attainment of high integration compared with devices using compound semiconductors such as GaAs. One reason is that the former can be formed on a Si substrate, which is inexpensive and also easily available as a large-diameter substrate. Another reason is that the former can be fabricated using the existing fabrication line for Si integrated circuits for which high integration technology has been established, in substantially the common fabrication process.
It has been found that a cross-contamination phenomenon arises when an attempt is made to fabricate a wafer for forming devices including a SiGe layer and a wafer for forming only MOS devices including no SiGe layer on the same fabrication line. This is a phenomenon that the SiGe layer acts as a contamination source and a device that does not include a SiGe layer, such as a Si device, is contaminated with Ge, whereby the characteristics of the Si device are adversely affected. The reason for this phenomenon is presumably that intrusion of Ge into the Si layer in an active region of a CMOS device or the like causes generation of an impurity level or the like that may serve as a trap or a recombination center.
In order to avoid the above problem, an exclusive line may be provided for devices including a component made of a Ge-containing material, such as a SiGe layer, a SiGeC layer, and a GeC layer, and distinctively separated from the fabrication line for general CMOS devices and the like. However, provision of a new fabrication line requires a great investment, and above all, this leads to loss of the advantage of the devices using a SiGe layer, a SiGeC layer, and the like of being able to use the common fabrication process with MOS devices.
In addition, in view of recent progress in system LSI and the like, it is presumed that a need will arise for fabrication of a xe2x80x9cconsolidatedxe2x80x9d device where a CMOS device and a SiGe device are formed in a common wafer. Expectation is therefore placed on establishment of a means for reliably preventing the cross-contamination phenomenon.
The object of the present invention is to provide a method for fabricating a semiconductor device in which a wafer including a Ge-containing semiconductor film and a wafer including no Ge-containing semiconductor film are fabricated using a common fabrication line as much as possible. This is attained by understanding the conditions under which the cross-contamination phenomenon arises and establishing a means for reliably preventing the cross-contamination based on the examination results
The first method for fabricating a semiconductor device of the present invention is a method for fabricating a semiconductor device including a Ge-containing semiconductor film using a common fabrication line for processing both a wafer including a Ge-containing semiconductor film and a wafer including no Ge-containing semiconductor film. The method includes the steps of: (a) substantially exposing the Ge-containing semiconductor film; (b) forming a cap layer having a function of blocking scattering of Ge in the air on the Ge-containing semiconductor layer; and (c) treating the wafer including the Ge-containing semiconductor layer at a temperature of 700xc2x0 C. or more after the step (b).
By adopting the above method, in the step (c), the high-temperature treatment at 700xc2x0 C. or more is performed in the state where the Ge-containing semiconductor film is covered with the cap layer. Therefore, Ge is blocked from scattering in the air even when this high-temperature treatment is per, formed on the common fabrication line. This means that when a wafer including no Ge-containing semiconductor film is to be processed on the common fabrication line, the wafer is suppressed from causing cross-contamination due to intrusion of Ge into the active region thereof.
Specifically, in the first method for fabricating a semiconductor device, any of the following procedures may be adopted.
The step (b) may be performed on a fabrication line separate from the common fabrication line, and the step (c) may be performed on the common fabrication line. This method is especially effective when the formation of the cap layer involves high temperature of 700xc2x0 C. or more.
Both the steps (b), (c) may be performed on the common fabrication line.
Alternatively, the steps (b), (c) may be performed on a fabrication line separate from the common fabrication line.
The method may further include the step of forming another cap layer on the existing cap layer. The additional cap layer is formed for fear that Ge may have been diffused even to a portion close to the surface of the first cap layer.
In the first method for fabricating a semiconductor device, when the temperature in the step (c) is in a range between 700xc2x0 C. or more and less than 750xc2x0 C., the cap layer may be made of silicon and may be formed so that a thickness W (nm) and a heat treatment time t (min) satisfy the relationship
Wxe2x89xa70.017xc3x97t.
In the first method for fabricating a semiconductor device, when the temperature in the step (c) is in a range between 750xc2x0 C. or more and less than 820xc2x0 C., the cap layer may be made of silicon and may be formed so that a thickness W (nm) and a heat treatment time t (min) satisfy the relationship:
Wxe2x89xa70.046xc3x97t.
In the first method for fabricating a semiconductor device, when the temperature in the step (c) is 820xc2x0 C. or more, the cap layer may be made of silicon and may be formed so that a thickness W (nm) and a heat treatment time t (min) satisfy the relationship:
Wxe2x89xa70.063xc3x97t.
The second method for fabricating a semiconductor device of the present invention is a method for fabricating a semiconductor device including a Ge-containing semiconductor film using a common fabrication line for processing both a wafer including a Ge-containing semiconductor film and a wafer including no Ge-containing semiconductor film. The method includes the steps of: (a) substantially exposing the Ge-containing semiconductor film; and (b) processing the wafer including the Ge-containing semiconductor film at a temperature of 700xc2x0 C. or more on a fabrication line separate from the common fabrication line after the step (a).
By adopting the above method, since the treatment at 700xc2x0 C. or more is not performed on the common fabrication line, scattering of Ge in the air is prevented on the common fabrication line. This means that when a wafer including no Ge-containing semiconductor film is to be processed on the common fabrication line, the wafer is suppressed from causing cross-contamination due to intrusion of Ge into the active region thereof.
In the second method for fabricating a semiconductor device, the method further includes the steps of: (c) forming a cap layer having a function of blocking scattering of Ge in the air on the Ge-containing semiconductor film after the step (b). Therefore, the subsequent process is performed with the existence of the cap layer in which Ge is scarcely diffused. This further ensures suppression of cross-contamination.
In the first or second method for fabricating a semiconductor device, the Ge-containing semiconductor film is preferably made of at least one of SiGe, SiGeC, GeC, and Ge.
In the first or second method for fabricating a semiconductor device, the cap layer is preferably made of at least one of silicon, silicon oxide, silicon nitride, and silicon oxynitride.